Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!sun-barr!decwrl!shelby!portia!drapeau@jessica.Stanford.EDU
From: drapeau@jessica.Stanford.EDU (George D. Drapeau)
Newsgroups: comp.windows.x
Subject: Question about Xaw Viewport widget
Keywords: (long), width, height, clip widget
Message-ID: <9518@portia.Stanford.EDU>
Date: 25 Feb 90 00:07:10 GMT
Sender: USENET News System <news@portia.stanford.edu>
Reply-To: drapeau@jessica.Stanford.EDU (George D. Drapeau)
Organization: Stanford University
Lines: 89


I have a question about the behavior of the Viewport widget in the R4
Athena Widget Set.  I've included a sample program that should
illustrate my problem, but let try to explain in English first.

The problem is that if I create a Viewport widget using
XtCreateManagedWidget (assuming that the Viewport's parent has already
been realized), then I get the following error:

	Error: Widget clip has zero width and/or height

If you look at the following code, though, I had already specified
both a width and height for the Viewport, but it doesn't seem to take
unless the Viewport has a child before it's realized.  In other words,
if I were just to make a Viewport then call "XtRealizeWidget", I'll
get the error.  But if I make a Viewport then insert a child into the
Viewport, *then* call "XtRealizeWidget", things will work fine.

I can't find anything in the "Athena Widget Set - C Language
Interface" doc that mentions anything about this constraint.  So is
this a problem with the Viewport, or did I miss something in the
documentation that says a Viewport will only have dimensions if a
child is inserted?

One more thing about the sample program:  if you move the call to
"XtRealizeWidget" after "myList" is created, the program should run
just fine.  As the program is included here, the program should
produce the error I described.

Help and/or clarification would be much appreciated.  Working around
this is fine, but I want to get the conceptual model correct (and see
where I failed to read).

Thanks in advance,

	George


Here's the sample program to illustrate my problem:
------------- cut here -------------
#include <X11/Intrinsic.h>
#include <X11/StringDefs.h>
#include <X11/Xaw/Viewport.h>
#include <X11/Xaw/List.h>

#define HELPSIZE 2

  char *listStrings[HELPSIZE] =
{
  "First List Item",
  "Second List Item"
  };


void main(argc,argv)
     int	argc;
     char	**argv;
{
  Widget	topLevelShell,myList,myViewport;
  static Arg	listArgs[] = 
    {
      {XtNlist,(XtArgVal)listStrings},
      {XtNnumberStrings,(XtArgVal)HELPSIZE},
      {XtNverticalList,(XtArgVal)True}
    };
  static Arg	viewportArgs[] =
    {
      {XtNwidth,300},
      {XtNheight,400},
      {XtNallowVert,(XtArgVal)True}
    };
  
  topLevelShell = XtInitialize("widgetTest","TestApp",NULL,0,&argc,argv);
  myViewport = XtCreateManagedWidget("myViewport",
				     viewportWidgetClass,
				     topLevelShell,
				     viewportArgs,XtNumber(viewportArgs));
  XtRealizeWidget(topLevelShell);
  myList = XtCreateManagedWidget("myList",
				 listWidgetClass,
				 myViewport,
				 listArgs,XtNumber(listArgs));
  XtMainLoop();
}

______________________________________________________________________________
George D. Drapeau			Internet: drapeau@jessica.stanford.edu
Academic Information Resources
Stanford University